1. Field of the Invention
The present invention relates to a fixation method for an optical member, such as a photographic lens, in which the optical member is joined and fixed to a holding member using laser welding, and also relates to an optical unit having such an optical member fixed.
2. Description of the Related Art
In conventional optical apparatuses, such as still cameras or video cameras, a variety of methods for fixing a lens have been employed. In recent years, since the size of a still camera or video camera has become smaller and a space usable for fixing a lens has also become smaller, a method for fixing a lens using adhesives is generally employed. Moreover, a method for fixing a lens using so-called thermal caulking in which a part of a lens holder is thermally deformed is also known.
However, in the case of the method for fixing a lens to a lens holder or the like using adhesives, which is generally employed, the adhesive may intrude into the effective diameter of the lens or may protrude from the lens holder, thus causing difficulty in production control. In addition, contraction of the adhesive being cured may distort the lens. Furthermore, the amount of applied adhesive may vary with the applied positions, thereby causing distortion of the lens, so that a desired optical performance may not be obtained. Furthermore, while an ultraviolet curable resin can be taken as an example of an adhesive usable for bonding an optical element, such as a lens, the time of irradiation of ultraviolet rays required to cure the ultraviolet curable resin is several seconds to several tens of seconds. It takes further time to completely cure the adhesive. Therefore, even if the position of a lens is adjusted, for example, by the correction for decentering, the lens position may gradually vary due to the unevenness of contraction of the adhesive until the adhesive is completely cured. Accordingly, the lens position may deviate from a desired position. Furthermore, in the case of a plastic lens, the lens may become yellowed by the intense irradiation of ultraviolet rays. Therefore, the color balance of the lens may vary.
In the fixation method using the thermal caulking, heat is also conducted to portions other than that required to be heated. Therefore, a portion of the lens holder other than a portion required to be heated may be deformed. If the lens or the lens holder is reduced in size and portions for mounting other parts are close to each other, the influence of heat further increases. If heat is excessively conducted to the lens, the lens may be deformed.
As a method for solving the problems with the bonding by the ultraviolet curable resin or with the thermal caulking for fixing a lens, Japanese Laid-Open Patent Application No. 2004-20867 discloses a technique of fixing a lens to a part, such as a lens holder, using laser welding. In this technique, a laser beam is radiated to a lens holder, a viewfinder holder or the like, which is made of plastic, so as to fix a plastic lens thereto.